The long-term goal of this project is to understand how the arylhydrocarbon receptor (AhR) and estrogen receptors (ERs) interact to regulate sexual differentiation of neural functions. We will use the AhR- and ER-rich anteroventral periventricular nucleus (AVPV) as a model to study such interactions. In rodents, sexual differentiation of the AVPV occurs during perinatal life when E2 synthesized in the male AVPV triggers apoptosis, thereby decreasing the size of the adult male AVPV and abolishing the potential for luteinizing hormone (LH) surge release. Developmental exposure to TCDD blocks apoptosis in the male AVPV and prevents defeminization of the LH surge mechanism. To understand how ER and AhR interact in the differentiation process, we used expression microarrays and identified CUG triplet repeat binding protein 2 (Cugbp2) as an AVPV gene that differs between males and females and is oppositely regulated by E2 and TCDD. Cugbp2 is an RNA-binding protein that regulates cyclooxygenase 2 (Cox2) mRNA translation and decreases Cox2 protein levels. Cox2 up- regulates Bcl2, a pro-survival protein that is higher in the female than in the male AVPV. In these exploratory studies, we will test the following hypothesis: E2 upregulates Cugbp2 mRNA and protein levels in GABAergic neurons of the developing male AVPV. Thus, Cox2 protein levels decline and this reduces Bcl2 expression and increases apoptosis. TCDD interferes with E2 upregulation of Cugbp2 expression in the AVPV and prevents apoptosis and defeminization. To test this hypothesis, we will verify that E2 and TCDD oppositely regulate Cugbp2 in GABAergic neurons in vivo and in vitro. We will also determine whether E2 and TCDD act through Cugbp2 to regulate Cox2 and Bcl2 expression, as well as downstream caspase 3 and 7 activity important for apoptotic cell death. Our findings will provide new insights into how E2 and TCDD regulate sexual differentiation of neural functions. Moreover, Cugbp2 has recently been implicated in late-onset Alzheimer's disease and also shown to play a role in neuronal apoptosis after global ischemia and reperfusion. Thus, our findings will provide new insights into how E2, and perhaps TCDD, affect neural disease and damage. Finally, our investigations of E2 and TCDD regulation of Cugbp2 may identify RNA binding proteins as important new targets through which AhR and ERs regulate cellular functions.